Wranglers only have "PART-TIME" 4WD, some other Jeep models use transfer cases that have both PART-TIME and FULL-TIME capabilities. Here are 2 examples, and there are actually even more than that.
NP231 - "Command-Trac" part-time only - 2.72:1 ratio low range
- shift pattern 2H - 4H - N - 4L
NP242 - "Selec-Trac" part-time
OR full-time - 2.72:1 ratio low range
- shift pattern 2H - 4part-time - 4full-time - N - 4L
Now to explain the difference between part-time and full-time gear selections.
This term describes when this selection should be used, only "part of the time" meaning when available traction is at it's worst & you need the most 4WD capability your Jeep has to offer.
This term describes when this selection may be used, which is "full time" meaning that you can drive it in this range 24/7 under any traction conditions.
Now to explain how these 2 selections work.
This selection makes a direct mechanical connection between the front & rear driveshafts, and does NOT
allow the power to be split at variable rates between the front & rear driveshafts. It operates much the same way a "locked" differential does, with regards to both axles being spun at the same speed. Using this selection on hard surfaces can cause "binding" in the transfer case & thus lead to premature wear and/or damage to the transfer case.
This selection also makes a mechanical connection between the front & rear driveshafts, but it DOES
allow the power to be variably split between the front & rear driveshafts. To make another axle differential comparison, this selection operates much the same way an "open" differential does, with regards to having the ability to direct the power to the 2 axles at different speeds. This allows the use of this selection on any surface & will not "bind" the transfer case.